Persistent infection of adult mink with the Aleutian mink disease parvovirus (ADV) leads to disturbances of immune regulation, including hypergammaglobulinemia, plasmacytosis, immune complex disease, interstitial and glomerulonephritis. The exceptionally high levels of antiviral antibody are not able to eliminate the virus. The major target cell population for viral replication and sequestration is macrophages. Infection of these cells is enhanced by anti-viral antibody (antibody-dependent enhancement of infection or ADE), but is somehow restricted at the level of the individual cell. This system has been modeled in vitro in the human macrophage-like cell line, K562. In newborn mink, however, ADV causes an acute fulminant interstitial pneumonia associated with severe respiratory distress. The major target cell in newborn mink is the type 2 alveolar epithelial cell, in which ADV replicates permissively. If antibody is present when newborn mink are infected, the acute disease is prevented and an attenuated form of the adult disease ensues. The permissive infection is modeled in CRFK cell cultures. Interestingly, antiviral antibody can neutralize ADV infectivity for these cells. A summary of this year?s studies includes: ? ADV infection in mink histocultures. To circumvent problems in the in vivo study of ADV infections, we developed a histoculture system in which slices of lymph node (LN) are grown in culture on collagen supports. These cultures maintain viability and recognizable cytoarchitecture for 5-7 days. Infection of the LN cultures with ADV-Utah yielded clear evidence of viral replication. Three days after infection ADV replicative form and virion DNA were observed by Southern blot; virion proteins, NS1 and NS2 were detected in the nuclei of infected cells by indirect immunofluoresence. Positive cells were located in the cortical region, but they could not be morphologically identified. ? Interrelationship between virus neutralization and ADE. Antiviral antibody neutralizes ADV infectivity for CRFK, but enhances infectivity in K562. Polyclonal sera from ADV-infected mink (#5114), a rabbit antibody against the loop 4 region of the viral capsid and a mouse monoclonal antibody (mAB #165) neutralized infectivity in CRFK cells, but enhanced infection for K562. These results suggested that the same antibody populations could mediate both effects. ? Isolation of mink primary blood mononuclear cells (PBMC). In order to study ADV infection in mink cells, a technique for isolation and culture of mink PBMC was developed. Following infection with in vivo derived ADV-Utah, both cytoplasmic and intranuclear staining for ADV antigens was detected between 3-5 days in a small fraction of the cells. Infection of PBMC with ADV-G may be enhanced in the presence of ADV-infected mink sera #5114 and mAB #165. ? Development of an ELISA for ADV. In order to facilitate monitoring of ADV infection in mink and analysis of new monoclonal antibodies, an ELISA was developed employing capsids expressed by recombinant baculoviruses. Antiviral titers in infected mink sera were 10-100 fold higher with the ELISA than with the traditional counter-immunoelectrophoresis (CEP) assay. Several mABs that were positive in ELISA scored negative in CEP, suggesting that antibody binding to ADV capsids may be very complex.